In recent years, enhance security has been sought for information appliances. In particular, portable information appliances such as cellular phones, smartphones or tablet-type or note-type personal computers have a high risk of being misplaced or stolen. For this reason, portable information appliances must have a highly-reliable personal authentication function.
For such demands, a biometric authentication technology in which, based on a biometric image containing biometric information such as vein pattern of a hand or a finger, fingerprint or palmprint, a user of a device or a system is authenticated has been developed. In biometric authentication technology, biometric information of a user is utilized for personal authentication. For this reason, it is difficult for a person other than a user to utilize without permission from the user an information appliance having a personal authentication function employing a biometric authentication technology having a sufficiently high authentication accuracy.
On the other hand, regarding portable information appliances, in order to miniaturize the device, the device may have a limited hardware resource in some cases. Since portable information appliances are powered by an internal battery, the information appliances are equipped with a processor having a small power consumption. A processor having a small power consumption has a relatively low throughput. In order to not compromise the convenience of portable information appliances, a biometric authentication process is preferably completed in a short time. For this reason, a biometric authentication technology in which the authentication accuracy is high and the load on a processor is small is demanded for portable information appliances. For the purpose of fulfilling such demands, a variety of biometric authentication technologies have been proposed (for example, see Japanese Laid-open Patent Publication No. 2004-21615, Japanese Laid-open Patent Publication No. 2009-31986, Japanese Laid-open Patent Publication No. 2005-149455, and Japanese Laid-open Patent Publication No. 2006-221256).
For example, in the technique disclosed in Japanese Laid-open Patent Publication No. 2004-21615, partial images of a subject acquired in a predetermined order are matched with a plurality of preregistered partial images in accordance with the acquisition order.
In the technique disclosed in Japanese Laid-open Patent Publication No. 2009-31986, a matching target body part in a finger vein pattern is randomly determined in response to an authentication request. A portion of the finger vein pattern corresponding to the matching target body part is matched once or a plurality of times with a corresponding portion of a finger vein pattern stored in a vein database. When the entire finger vein pattern is matched, for a finger matched by using a portion of the finger vein pattern, matching is performed once or a plurality of times by using the whole finger vein pattern to be authenticated when all are matched.
Further, in the technique disclosed in Japanese Laid-open Patent Publication No. 2005-149455, the feature value of each partial image for each of two images is determined. For each partial image in one image, the position of a partial image which has the maximum degree of matching therewith in the other image is then searched. The similarity between the two images is calculated based on information relating to the partial region whose a positional relationship quantity is in a predetermined range. The positional relationship quantity represents a relationship between a reference position for measuring the position of a partial region in one image and the position of the other image corresponding to the partial region which has the maximum degree of matching. Based on the similarity, it is judged that two images match each other or not.
Further, in the technique disclosed in Japanese Laid-open Patent Publication No. 2006-221256, a pattern information is extracted from each of a plurality of images. Each extracted pattern information is sequentially matched with registered pattern information, and the matching process is stopped when a matching result is obtained in which the extracted pattern information represents the authentication target corresponding to the registered pattern information.